1. Field of the Invention
The present invention relates to a dynamic sensor including a piezoresistive element, and in particular, relates to a uniaxial-detection dynamic sensor.
2. Description of the Related Art
Various dynamic sensors using piezoresistive elements have been proposed. For example, in Japanese Unexamined Patent Application Publication No. 63-305256, such a dynamic sensor includes a weight having a rectangular parallelepiped shape, a support arranged so as to surround the weight, and beams rotatably supporting the weight on the support. The beams are provided on both opposing ends of the weight and formed in such a shape as to allow the weight to receive an external force to move.
FIG. 7 is a perspective view of an existing dynamic sensor 10P having the same structure as that of the dynamic sensor disclosed in Japanese Unexamined Patent Application Publication No. 63-305256. In FIG. 7, with regard to a support 12P, only portions connected to beams 13P are shown, and illustration of the other portion is omitted. In addition, the dynamic sensor 10P has an existing general structure, and thus only an outline of the structure will be described.
A weight 11P is formed in a substantially cubic shape. The beams 13P are connected to approximate centers of two opposing sides, respectively, of the weight 11P on the upper surface side. Each beam 13P is formed in such a shape as to allow the weight 11P to move in response to application of an external force. An end of each beam 13P on the side opposite to the side of the beam 13P to which the weight 11P is connected is connected to the support 12P. The weight 11P, the beams 13P, and the support 12P are integrally formed by, for example, etching a silicon substrate on which a piezoresistive element is formed.
However, in the dynamic sensor 10P having the existing structure as shown in FIG. 7, the following problem arises.
In the existing dynamic sensor 10P, when a force is applied in a direction parallel to an axis (an x-axis in FIG. 7) parallel to the two opposing sides on the upper surface side of the weight 11P to which the beams 13P are provided, the weight 11P oscillates about an axis connecting the two beams 13P (a y-axis in FIG. 7). In this case, as shown in FIG. 7, very small regions near corners at four portions where the beams 13P are connected to the weight 11P and the support 12P are stress occurrence regions 30P.
Here, when a physical characteristic such as acceleration due to an applied force is measured with a dynamic sensor, it is necessary to provide a piezoresistive element in each stress occurrence region 30P.
However, in the existing dynamic sensor 10P, each stress occurrence region 30P has a very small surface area, and thus it is not easy to precisely provide a piezoresistive element in this region. Conversely, it is not easy to realize a dynamic sensor that can accurately detect stress to more reliably measure a physical characteristic such as acceleration.